Home WTI User's Guides
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1. Introduction
2. Binary Block Read Mode and Structure
2.1. Compressed Binary Block Read Sequence
2.2. Compressed Binary Block Structure
2.2.1. Data Block Structure
2.2.2. Record String Structure
3. Compression Decompression Methods
3.1. Table Decompression
3.1.1. Nibble Positioning
3.1.2. Record String Format
3.1.2.1. Data Decompression Considerations
3.1.3. Table Decompression Example
3.2. Space Compression
4. DLE Stuffing
5. The Cyclic Redundancy Check Option
5.1. Calculation
6. Customer Service
PollCat Series

4. DLE Stuffing

 

PollCat uses the Data Link Escape (DLE) function to pass literal characters within a string of binary data. After binary data is transmitted, the receiving device can then pick the literal characters out of the string. The DLE function is necessary because of the nature of eight bit binary data; literal characters can occur randomly anywhere in the binary data string. Without a means of recognizing the actual characters, the polling device would trigger on these false characters. This function is optional and when set, is only used in Compressed Binary Block Mode.

DLE Stuffing is the last function performed before transmission. Therefore, the reverse function should be the first task performed when data is received. When using the DLE Stuffing function, the following points must be considered:

•                      DLE Stuffing characters are not included in the CRC calculation.

•                      DLE Stuffing is not performed on the CRC characters themselves.

•                      DLE Stuffing characters are not included in the character count.

 

The DLE stuffing and unstuffing functions are performed as follows:

1                     If the DLE option is selected, PollCat inserts a DLE character (10 HEX) into the data string at transmission time. The DLE character precedes any character the receiving device will recognize as a literal character.

2                     The DLE character is inserted prior to the starting STX character, the ending ETX character, and each DLE (10 HEX) character that may occur in the binary data. The stuffing DLEs in front of the data DLEs are needed in order to ensure that data DLEs are actually received as data, and are not mistaken for stuffing characters themselves.

3                     Each time a DLE character is received by the polling device, it is discarded and the next character is taken as a literal character.

4                     Using the DLE function, the receiving device can pick out the STX and ETX characters without mistakenly flagging on binary data, which may randomly match these characters.